1. Field of the Invention
The present invention relates to a polymer composition for electrical part material.
2. Description of Background Art
Along with development of high frequency-related technologies, there is a tendency that a wider frequency band is used for equipments for signal transmittance. Some equipments are designed to receive or transmit signals with a frequency in the range of several hundred megaheltz (MHz) to several hundred gigaheltz (GHz). Materials used in electrical equipments using high frequency, specifically, materials used for devices or parts, such as packages, wiring circuit board substrates, sockets, and connecters, as well as materials for connecting these devices or parts, must have excellent electrical characteristics, such as a low dielectric constant and a low dielectric dissipation factor. The electric loss also must be small.
Beside the excellent electrical characteristics, superior moldability and metal platability are also required for electrical insulation materials, particularly those using high frequency.
Polyether imide, polyester, polyimide, and the like are popular engineering plastics due to their high heat resistance, excellent electrical insulation, and superior mechanical properties. These are also widely used as electrical insulating materials such as IC substrates and printed wiring board substrates because of their excellent heat resistance and electrical insulation.
These condensed aromatic-type heat-resistant polymers, however, exhibit only limited performances as insulating materials for high-density, multi-layered, integrated circuits or high-speed, high-frequency circuits due to their comparatively high dielectric constant and dielectric dissipation factor.
On the other hand, polyphenylene ether, polyolefin, polycarbonate, aromatic polyvinyl compounds, and the like have a low dielectric constant, dielectric dissipation factor, and other excellent electrical properties, although these are inferior in the mechanical properties, and heat resistance.
A number of studies are being undertaken on the design of polymer blends for the purpose of obtaining materials exhibiting two or more excellent characteristics possessed by these different-types of polymers.
A serious problem in these polymer blends is incompatibility of the component polymers. A number of polymers are incompatible each other, which is a cause of inferiority of various characteristics, especially mechanical properties.
For increasing the compatibility between polyether imide and polyphenylene ether, each having excellent characteristics as mentioned above, Japanese Patent Laid-open (kokai) No. 32880/1993 proposes incorporation of an epoxy-modified aromatic vinyl resin to the polymer blends as a compatibilizer.
Although epoxy-modified aromatic vinyl resin used in the Japanese Patent Laid-open (kokai) No. 32880/1993 as the compatibilizer can promote interactions among polymers, this resin is inferior in the heat resistance by itself. If used in a large amount in a polymer blend comprising polyether imide and polyphenylene ether, it may impair excellent heat resistance inherently possessed by the former polymers.
In addition, because this compatibilizer has a lower crystalline or glass transition point than that of polyether imide and polyphenylene ether, the three-component polymer blend may result in unhomogeneous molded articles with a surface layer consisting of the compatibilizer, if it is used in a large amount.
This unhomogeneous property may a cause of decreased heat resistance, electrical characteristics, and mechanical characteristics, especially when the molded articles are prepared by repeated melting operations.
In the case of electrical insulation materials used for electrical parts, e.g., IC board substrates or printed circuit board substrates, etc., high thermal conductivity is desired for efficiently dissipating heat generated during the time when these are used, in addition to excellent characteristics such as heat resistance, mechanical characteristics, electrical insulation properties, dielectric properties, and moldability.
However, because polymers generally have only small thermal conductivity, improvements in the conductivity is difficult if components for the blend is limited to polymers. Thus, this prior art composition remains insufficient with respect to thermal conductivity.
An object of the present invention is therefore to solve the problem of the poor compatibility among polymers without causing the above-mentioned problem of unhomogeneity in the molded articles, and to provide a polymer composition for use as an electronic material suitable for use at a high frequency range, which exhibits not only excellent electrical insulation, dielectric properties, heat resistance, mechanical characteristics, and moldability, but also superb heat characteristics such as thermal conductivity, and yet capable of excellently molded even if the same may be repeatedly molded.
The present inventors have undertaken extensive studies in order to achieve this object, and found that a combination, at a specific proportion, of (I) a polymer blend which comprises (A) at least one polymer selected from specific types of polyether imides and polyesters, and (B) at least one polymer selected from specific types of polyphenylene ethers, polyolefins, and polycarbonates, and (II) a copolymer of maleic anhydride and vinyl type compound, and, optionally, (III) fillers and the like, can provide a composition (hereinafter referred to as the first composition) with excellent compatibility, heat resistance, mechanical characteristics, metal platability, and moldability, while exhibiting superior electrical characteristics, such as reflecting and passing properties, i.e., a small return loss and a small insertion loss.
The inventors have further found that (I) said polymer blend, if combined with a very small amount (0.1-1.0 parts by weight for 100 parts by weight) of (II') an epoxy-modified styrene-type copolymer, especially a grafted epoxy-modified styrene copolymer, and, optionally, (III) fillers and the like, can provide a composition (hereinafter referred to as the second composition) with the same excellent characteristics as the first composition. This finding was surprising in that there is no decrease in the compatibility even though the amount of the epoxy-modified styrene-type copolymer is very small, and also there is no problem of unhomogeneity even though the composition is repeatedly molded.